Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$74.66	7.368%	$80.1609	$80.16	$80.15	$80.20
Purchase #2	$120.32	9.567%	$131.831	$131.83	$131.85	$131.80
Purchase #3	$112.67	5.455%	$118.8161	$118.82	$118.80	$118.80
Purchase #4	$77.31	8.251%	$83.6888	$83.69	$83.70	$83.70
Purchase #5	$207.83	12.121%	$233.0211	$233.02	$233.00	$233.00
Purchase #6	$168.35	11.270%	$187.323	$187.32	$187.30	$187.30
Purchase #7	$190.86	6.821%	$203.8786	$203.88	$203.90	$203.90
7 purchase totals =	$952.00		$1,038.7195	$1,038.72	$1,038.70	$1,038.70